The high potential of ground-source heat pumps to decarbonise the European building sector
A potential reduction of 20-40% and 30-50% of energy demand in buildings, for heating and cooling respectively, could be achieved through increased use of geothermal heat pumps.
According to a recent review article (1), in the European Union, 40% of the overall final energy consumption is attributable to the buildings sector. One reason for such high ratio is that the great majority of the building stock is over 40 years old. According to the European Commission, an interesting potential lies in the refurbishment of the building sector, and heat pump technology has been recognised as one of the most cost-effective solutions to tackle the environmental issue in this sector. One of the main strengths of heat pumps is their capability of generating both heating and cooling with the same device.
In recent years, the heat pump market has experienced strong growth: in EU countries, 1.6 million heat pumps were installed in 2020, 5% up with respect to 2019 despite shortages due to the COVID-19 crisis, with Italy, France and Spain leading the sector.
The vast majority of heat pumps installed are aerothermal, mainly in Mediterranean countries, while ground source heat pumps (GSHPs) are widely used in countries with cold climates. In Italy, the leading European country in terms of installed heat pumps , air source heat pumps (ASHPs) occupy 97% of the market, while GSHPs only represent 3%.
However, despite significant expansion, heat pumps cover only a small share of the overall heat generator market. A relevant reason is the practical infeasibility of retrofitting a space-heating system without replacing radiators, which represent over 90% of the existing heat terminals in households.
From this perspective, GSHPs are able to keep high efficiency and performance even at high heat sink temperatures, making this technology an interesting solution for retrofitting buildings without replacing existing heat terminals.
In addition, GSHPs, whose efficiency and capacity depend on the ground temperature, benefit from a more stable cold source with a temperature level generally higher than the ambient temperature in winter and lower in summer, thus achieving a higher energy efficiency (up to 20%) than ASHPs in identical conditions.
Currently, the high initial investment cost necessary for the installation of the equipment is the main obstacle to a wider diffusion of GSHPs in residential applications. Drilling and piping costs cover a significant part of the total installation cost, between 20% and 60%. To date, the payback time for the investment is 5-10 years.
A reduction of 20–40% and 30–50% - respectively for heating and cooling - of the energy demand in buildings could be achieved with GSHPs, together with a reduction of CO2 emissions by 15% to 77%, considering residential and non-residential buildings.
In order to exploit the high potential of GSHPs, it is therefore essential to make this technology cheaper and more cost-effective.
The authors stress the importance of further research into more cost-effective heat pumps and more compact and easier to install borehole heat exchangers. The latest advances concern pipe materials, grout materials, refrigerants and secondary fluids where micro phase-change materials show promising results. Finally, great attention must be paid to proper design and control of the plant, in order to guarantee low operating costs and to limit investment costs.
(1) Menegazzo D. et al. State of the Art, Perspective and Obstacles of Ground-Source Heat Pump Technology in the European Building Sector: A Review. Energies, vol. 15, issue 7 (Article available in FRIDOC thanks to an agreement with MDPI).